What is the commom error for entering 1098-T?

I'll see if @Hal_Al knows. Otherwise contact Support.

How do I contact TurboTax? (intuit.com)

There's no simple answer. You could try deleting the 1098-T and starting that part over.

Go through the entire education interview until you reach a screen titled "Your Education Expenses Summary".  Click delete next to the student's name.  You'll then get the "Your Education Expenses Summary" screen again.  Click the "Add a student" button.